A display device which is worn on the head and is used to view video, i.e., a head-mounted display (HMD), is well known (see, for example, Patent Literature 1, etc.). A head-mounted display has an optical unit for each of the left and right eyes, and is also used in combination with headphones, and is thereby configured to be capable of controlling visual sensation and auditory sensation. There have recently been advances in techniques for a so-called see-through head-mounted display, which allows the user wearing the display to see a real scene at which the user's line of sight is aimed.